Brian, Yes this is a PCT hospital, in sunny Dorset.
The plot thickens with this door.
The door is on automatic magnetic hold open during the day.
At 16:00 the door is released automatically and closed
This is to prevent visitors, and unsavoury persons from entry to an area of the hospital which is unmanned from 16:00. However staff still need access to this area and have electronic key fobs to open the door.
Visitors use the green box to open the door.short cut to car park after 16:00
The idea of a switch operated by a special key sounds interesting, because that facility is already fitted ie the staff electronic key fob system.
Anyway risk assessment tells me we would not require the exit at night for fire evacuation.
Im going down the route to have the box removed.
The door will release on activation of a MCP or detector
Thanks for the the advice, with fire alarm companys telling us we need green buttons, breakglass boxes, override switches, linked to fire alarms, HTMs, and all the other legislation it becomes confusing and expensive. Risk assessment is great idea but scary when you have no one for a second opinion